Bypass Trim - BOMBARDIER LEARJET 40 Pilot's Manual

Electrical power for primary pitch trim is provided by the L ESS BUS
and is protected by the TRIM-PRI PITCH circuit breaker located on the
pilot's circuit breaker panel (FLIGHT group). The dc electrical power to
the #1 IC is also required for primary pitch trim, except for primary by-
pass trim. The power for #1 IC is provided by the L ESS BUS and is
protected by IC/SG 1 circuit breaker located on the pilot's circuit
breaker panel (INSTRUMENT/INDICATIONS group).

Bypass Trim

Primary trim reverts to bypass as a result of a detected malfunction or
#1 IC failure and cannot be selected by the crew. When in bypass trim a
fault is displayed on CAS and control wheel trim switch commands go
directly to the primary trim actuator, bypassing the IC circuits. The #1
IC trim functions (IC controller/monitored primary trim, configuration
trim, and Mach trim) are all disabled in this case. When in bypass trim,
the primary trim actuator operates at only two speeds (high or low).
The speed depends on flap position. Dual flap position inputs are pro-
vided to the actuator electrical box to maintain redundancy. If the flap
signals do not agree, the rate of trim function is limited to slow speed.
Both flap signals must agree and must indicate flaps are greater than 3°
for the actuator to operate at a high rate. When the flaps are up (<3°),
primary bypass trim will be at a slow rate. The primary trim actuator
continues to monitor for uncommanded trim and incorrect trim direc-
tion in the bypass trim mode. It also monitors for the correct trim speed
based on flap position. If it detects a failure in any of these areas, prima-
ry trim is disabled and a fail CAS is displayed.
The following CAS illuminations are specific to the primary pitch trim:
CAS
PRI TRIM FAIL
PRI TRIM FAULT
PM-132A
Color
Amber The primary pitch trim system has failed.
White The Integrated avionics Computer (IC)
detects a fault in the primary pitch trim
system.
Pilot's Manual
Description
5-17